​PPDL Picture of the Week

May 28, 2018

Pests and diseases of berries in the home garden.

Bruce Bordelon, Professor, Department of Horticulture and Landscape Architecture

Strawberries are among the most popular fruit to grow in the home garden. They take up little space, produce fruit one year after planting, and provide a generous supply of tasty berries for a month or more (Picture 1). Red raspberries are another popular home fruit. While they take a bit more space, they are easy to grow and provide  plenty of fruit throughout the summer, and into fall if you have primocane fruiting types (Picture 2). However, anyone who has tried to grow fruit at home knows that it is difficult to produce berries that are as perfect as we find in the grocery store. Some of the most common problems of locally grown berries are damaging pests and diseases. Of particular concern during harvest are slugs, sap beetles, and Botrytis gray mold.

Botrytis gray mold is a diseased caused by the fungal pathogen Botrytis cinerea. Botrytis is a common saprophyte and pathogen of a number of fruit and ornamental crops. In strawberries and raspberries, the fungus invades during bloom and usually infects the dying petals or stamens. The fungus remains latent until the fruit begins to ripen then progresses into the ripening berry to cause a rot. In strawberries, you often find infections starting at the top of the berry near the cap, where the dying flower parts remain (Picture 3). In raspberries, the disease can be particular serious following a few days of rain, especially on fall bearing types. (Picture 4)

Sap beetles (Stelidota geminata), are a common pest, especially of strawberries. The adult beetles invade the plantings as the fruit ripens and feed on berries, leaving deep cavities and tunnels. This damage often leads to development of secondary rots (Picture 5). The adult beetles are small, about 1/8 inch long, oval, and mottled brown in color (Picture 6). They are difficult to see because they usually drop to ground when disturbed. Growers are often surprised by the size of the cavities considering the small size of the beetles. We often hear complaints of bird pecking, but I suspect most of the damage we see is from sap beetles, not birds.

Picnic beetles (Glischrochilus species) are another potential pest of berries. They are more common on raspberries, but are opportunists and can be found feeding on strawberries as well. The adults are larger than sap beetles, about ¼ inch long, dark in color, usually with four orange spots on the back. One distinguishing characteristic is that they have knobbed antennae (Picture 7). They are quite common on red and yellow raspberries (Pictures 8 and 9).

Slugs (Deroceras species) are molluscs, not insects. But they cause damage to strawberries that resembles damage from sap beetles. They chew deep holes in the surface of the berries, especially under the cap. Those found is strawberries are usually small, less than one inch long, though certain specimens can be much larger.

Control: Sanitation is the key to managing pests and diseases in the home strawberry planting. Since beetles are attracted to overripe fruit, pick often and discard all damaged fruit away from the planting. Keep berries from direct contact with soil by maintaining a layer of straw mulch. One complication is that mulch also provides an ideal habitat for sap and picnic beetles and slugs. One way to help is to keep the strawberry rows narrow with some bare between. This will allow the surface to dry. Use of insecticides for sap beetles and slugs is not recommended due to the frequent harvests. Bait buckets containing overripe fruit and a bit of soapy water can be very effective at trapping beetles. For Botrytis, if fungicides are considered, they should be applied during bloom when infections are likely to occur. Application near harvest is not effective at controlling the disease.

Sanitation and vigor management is helpful for raspberries. Keep the rows relatively narrow at the base, control weeds to provide an open canopy environment, and do not apply more fertilizer than the plants need. As with strawberries, for Botrytis control, any applications of fungicide should be during bloom.

More information about strawberry pests can be found in ID-146 Managing Pests in the Home Fruit Planting. https://mdc.itap.purdue.edu/item.asp?item_number=ID-146-W​

​​Click Image to enlarge

 

Picture 1: Strawberry harvest from a few feet of row.

Picture 2: Hand full of nice red raspberries.

Picture 3: Gray mold on strawberry.  

Picture 4: Gray mold on red raspberry.

Picture 5: Picnic beetle on a damaged strawberry. Note the sporulation from gray mold beginning to develop on the sunken lesion, and the dead stamens on the cap near where the infection started.  

Picture 6: Sap beetles on strawberry.

Picture 7: Picnic beetle on strawberry. Note clubbed antennae.

Picture 8: Picnic beetles on red raspberry. Note four orange spots on back.

Picture 9: Picnic beetle on yellow raspberry. Note orange spots and clubbed antennae.